We're going to the Dominican Republic for our honeymoon from St. Lucia. FI wanted Aruba, but it costs the same to fly there from St. Lucia as it does from New York, so we decided to hold off on that island.
I had no intention of going to the DR, but I fell in love with Excellence Resort, so that's why we're going there. Since we didn't care what island we went to, I just started researching resorts. We narrowed it down to a few top choices and then looked at how easy/difficult it would be to get there from St. Lucia and what the cost would be. What helped was that we are flying with the same airline the entire time, so we saved money by doing a multi-city reservation.
As a side note, you're probably wondering why we're not staying in St Lucia. I'll be there for a week before the wedding and we just went there last October, so we wanted to try a new place. I HIGHLY encourage you to look into St. Lucia though. I love it there.